Generally, when completing a subterranean well for the production of fluids, minerals, or gases from underground reservoirs, several types of tubulars are placed downhole as part of the drilling, exploration, and completions process. These tubulars can include casing, tubing, pipes, liners, and devices conveyed downhole by tubulars of various types. Each well is unique, so combinations of different tubulars may be lowered into a well for a multitude of purposes.
When placing any type of tubular downhole there is a risk that it can get stuck in the well. This can happen for several reasons including: the well has partially collapsed, operator error, or due to the geometry of the drilling path. Once the tubular becomes stuck, a variety of non-destructive means are available for the operator of the rig to try and free the tubular. These include rotating the tubular, jolting the tubular, or simply pulling up on the tubular until it comes free. However, if these options are unsuccessful then the operator might have to resort to using a cutting or severing tool such as a jet cutter to cut the tubular.
Tubulars may also be cut in abandonment operations. Abandonment operations are increasingly subject to regulations to provide for minimizing the long term environmental impact of abandoned wells. An operator will often times have to remove miles of tubulars while contending with cemented equipment, damage in the wellbore, or other unforeseen difficulties. The jet cutter is a critical tool that allows the operator to cut and retrieve tubulars from the well. The demand for cleaner abandoned wells, in conjunction with the growing number of idle wells in general, is a driving force in the market for jet cutters.
A jet cutter is an explosive shaped charge that has a circumferential V-type shape. The explosive is combined with a liner. The components are all contained in a housing. The jet cutter is lowered to the desired point where the separation of the tubular is desired. When the jet cutter is detonated, it will generate a jet of high energy plasma, typically in 360 degrees of direction, that will severe the tubular. Afterwards, the upper portion of the tubular is pulled out of the well. Then the operator can use a fishing tool to remove the still stuck lower portion of the tubular.
While other types of tubular cutters are available, including mechanical cutting devices and chemical cutters, the focus of this invention is on explosive shaped charge jet cutters that are widely used throughout the oil industry. Jet cutters have increased in popularity due to improvements in reliability and the increased use of horizontal wells.
A shaped charge is a term of art for a device that when detonated generates a focused explosive output. This is achieved in part by the geometry of the explosive in conjunction with a liner in the explosive material. Many materials are used for the liner, some of the more common metals include brass, copper, tungsten, and lead. When the explosive detonates the liner metal is compressed into a super heated, super pressurized jet that can penetrate metal, concrete, and rock.
Shaped charges must be transported from a manufacturing facility to the field. The high explosives must be maintained and designed such that the risk of any premature or unintended detonation is mitigated against. Shaped charges are transported by a variety of transportation methods, in all climates and temperature ranges, and may be subject to temperature variations, vibrations, mishandling, and fire. They often have to travel across multiple legal boundaries, with varying safety requirements.
One of the safety requirements is that if the shaped charge is in a fire, it will not detonate but instead will burn or deflagrate. This requires that pressure buildup within the housing is minimized while the explosive material is burning. A rapid buildup in pressure while burning could lead to detonation of the shaped charge.
A common method of retaining the explosive material inside a shaped charge is to use an adhesive to hold the explosive, liner, and housing intact. Under deflagration, this adhesive may melt and not constrain the gases building up in the housing from escaping. The problem with using an adhesive is that it must be applied during the assembly process of the shaped charge, adding extra manufacturing costs. Also, the adhesive is susceptible to shock and heat, thereby compromising the assembled shaped charge, especially during shipping and storage.
Shaped charges contain many components that must be held into place effectively. Several methods for retaining the shaped charge components will restrict the ability of the shaped charge to vent gases in the event that the shaped charge begins deflagrating due to a fire. In order to meet safety and transportation requirements, the shaped charge must be designed such that in the event the shaped charge catches fire, the gases produced from the deflagration will safely vent out of the tool without excessive pressure buildup. However, providing operators with the level of quality necessary for cutting without adversely affecting the well requires all the components to be precisely positioned within the tool.
Current methods for allowing a shaped charge to deflagrate safely during transportation include shipping the shaped charge partially disassembled. This can include shipping the shaped charge in multiple pieces or simply leaving out o-rings that seal the housing. This option is not ideal because it requires some form of post-shipping assembly to prepare the shaped charge for use. This reduces the quality control from the manufacturer's perspective because some form of assembly work is being performed outside of the manufacture's control. There is a risk that incorrect operator training, conditions at the well site, or other unforeseen difficulties will result in a faulty assembly that affects performance of the tool or even causes a premature detonation.
A manufacturer of shaped charges would prefer to have the entire assembly process, from start to finish, occur in its facilities where the proper safety protocol and manufacturing techniques are known to be used. This reduces the failures in the field and provides the customer with a finished product ready for use, with a known quality. Therefore, a need exists for new designs in shaped charges that can allow for safely shipping a fully assembled product, ready to use, that complies with various licensing requirements.